1. Field of the Invention
This invention relates to wet strength resin compositions and a method for making them.
2. Description of the Related Art
Polyamine-epichlorohydrin resins have been used as wet strength resins for paper since the early 1950's. These resins are cationic by virtue of the fact that they contain quaternary ammonium functionalities and are, therefore, substantive to negatively charged cellulose pulp fibers. These resins are particularly useful because they are formaldehyde-free and develop wet strength at neutral or alkaline pH values. The polyamine-epichlorohydrin resins are normally made by reacting epichlorohydrin and a polyamine such as ethylenediamine, triethylenetetramine, bishexamethylenetriamine, and amine still bottoms which is a mixture of polyamines containing from about 35% to about 70% by weight bishexamethylenetriamine. While the reaction is usually carried out in water, U.S. Pat. Nos. 3,894,944; 3,894,945; Re. No. 28, 807; 3,894,946, 3,894,947, disclose that a water soluble alcohol may be used in place of part of the water. However, these patents also disclose that it is generally preferred to use water alone for economic reasons. U.S. Pat. No. 2,595,935 discloses the use of a water miscible solvent such as ethanol. The use of simple alcohols such as methanol and ethanol as cosolvents has been found to be unacceptable when polyamine-epichlorohydrin resin solutions are used as wet strength resin compositions because these alcohols have low flash points and they remain in the final product. It would be desirable, therefore, to use an alcohol that has a flash point high enough for use in commercial paper making operations and one that is not a health and safety hazard to those who handle it or those who use products produced by wet strength formulations containing it.